The invention relates to a hazardous material detection system and, more particularly, to a hazardous material detection system well suited for use in detection of nitro compounds etc. that have a nitro group having a low saturated vapor pressure.
At an airport and other public facilities, it is attempted to install a hazardous material detection system that detects a nitro compound having a nitro group as a hazardous material, to prevent it from being brought into the airplane or a building. In this kind of hazardous material detection system, an atmospheric pressure ionization mass spectrometer is employed which is provided with an ion source operable at the atmospheric pressure, to analyze mass of a gaseous sample (gas to be inspected) containing a substance stuck to an incomer to be detected.
The atmospheric pressure ionization mass spectrometer introduces the gaseous sample to a corona discharge section fitted with a corona discharge needle electrode and an extraction electrode, applies a high voltage between the needle electrode and the extraction electrode to give rise to corona discharge in order to ionize the gaseous sample, introduces the ioned gaseous sample to an analysis section to analyze its mass, and outputs an analysis result to a data processor. The data processor is arranged to decide whether the gaseous sample contains the hazardous material based on the analysis result from the atmospheric pressure ionization mass spectrometer and output a result of the decision.
When it is analyzed by the atmospheric pressure ionization mass spectrometer, the gaseous sample introduced to the corona discharge section may contain non-polar to highly polar substances contained in the atmosphere as well as a dust (SiO2) and an organic substance. Furthermore, introduced the gaseous sample contains a variety of miscellaneous substances including those having a low evaporation temperature through a high evaporation temperature. When the variety of substances contained in the gaseous sample is introduced to the corona discharge section, an inside of the ion source is contaminated and foreign matter such as silicon (Si) and carbon (C) sticks to the needle electrode and the extraction electrode. When the foreign matter sticks to the needle electrode and the extraction electrode, corona discharge becomes unstable, to deteriorate an ionization efficiency of a sample component as well. Especially if much foreign matter sticks to them, the gaseous sample cannot pass through pores in the corona discharge section, thereby disabling analysis. Therefore it becomes necessary to clean the needle electrode and the extraction electrode, thereby requiring additional time and labor.
To prevent contamination and clogging in the ion source, such a method has been proposed that, as described in Jpn. Pat. Appln. KOKAI Publication No. Hei 6-310090 and Jpn. Pat. Appln. KOKAI Publication No. Hei 10-125276, a liquid chromatograph mass spectrometer is provided with a pore electrode cleaner, to spray a washing solvent such as methanol, acetone, or water every constant time, thereby washing the pore electrode.
The method employed in the conventional technology of using such a washing solvent as acetone, methanol, or water to wash the needle electrode and the extraction electrode cannot sufficiently remove Si and C stuck to these needle electrode and extraction electrode. Moreover, the conventional technology can be applied to the liquid chromatograph mass spectrometer but not to an atmospheric pressure ionization mass spectrometer, which analyzes mass of the gaseous sample. Further, when such washing solvent as methanol, acetone, or water is used to wash the electrodes, the inside of the ion source section, which is heated to 200° C., is cooled down in a moment of time, thereby generating a cold spot. This causes in some cases sticking of dusts and organic substances in the gaseous sample, thereby clogging the pores.
That is, the conventional technology takes into account only washing the needle electrode and the extraction electrode if the inside of the ion source section is contaminated in connection with corona discharge but not suppressing occurrence of contamination due to ionization.